The purpose of this paper is to investigate the effects of pile head condition and pile length on the behavior of laterally loaded piles in sand. The tests were carried out on single piles by using test apparatus which was especially desinged to apply both of fixed and free head conditions. Based on the results of the model tests, Broms' assumption of the ultimate soil resistance equal to three times the Rankine passive pressure for sand is examined, and classifying into "long pile" and "short pile" modes in the method of the estimating ultimate lateral resistance of single piles is also discussed.